Under 35 U.S.C. xc2xa7 119 this application claims the benefit of co-pending Japanese Patent Application No. 2001-185900, which was filed Jun. 20, 2001, and is incorporated herein by reference.
Systems that store optical signals are key building blocks in optical communication systems and in optical computing systems. In general, optical signal storage systems enable optical signals to be modified (e.g., path alteration or signal reshaping), stored, and delayed. For example, an optical signal must be temporarily stored if the information in the signal is to be read out directly at a relay station within a network. An optical storage delay line also is needed to enable the waveform of an optical signal to be measured.
A variety of different optical memory systems have been proposed. For example, several types of serial optical signal storage systems have been demonstrated using recirculating optical fiber loops. These optical memory designs are either pulse-preserving, where the same optical pulses propagate on each circulation of the storage loop, or regenerative where the pulses are replaced after some number of memory circulations.
One type of optical memory system includes an optical fiber loop and a switch that couples optical signals into and out of the optical fiber loop. The optical switching function may be provided by an electrically-controlled optical switch or by an optical coupler. For example, U.S. Pat. No. 5,533,154 describes an optical memory in which optical signals may be written to or read from a loop mirror switch by an optical coupler that may be selectively changed between a reflecting mode and a coupling mode by a polarization controller. U.S. Pat. No. 6,035,081 describes an optical memory in which the optical switching element is an interferometric non-linear switch with an optical amplifier as the non-linear element. In this optical memory, the optical switching element is a terahertz optical asymmetric demultiplexer that is responsive to switching pulses from an optical source to allow data to be switched out of an optical loop.
U.S. Pat. No. 5,862,286 describes another type of optical memory device that includes two nonlinear optical media and two mirrors that are arranged to reflect light between the two nonlinear optical media. In this optical memory device, a first mirror reflects light passing through a first nonlinear optical medium and into the second nonlinear optical medium. The second mirror reflects part of the light reflected from the second nonlinear optical medium back into the first nonlinear optical medium.
The invention features a optical signal storage scheme that may be implemented in a device that has a relatively small size and is capable of maintaining high optical signal storage quality with relatively little signal attenuation.
In one aspect, the invention features an optical signal storage device that includes an optical memory loop and a substrate. The substrate carries an input optical port, an output optical port, an optical signal path that is coupled between the input and output optical ports, an optical memory path that is coupled to complete the optical memory loop, and an optical read/write controller that is coupled between the optical signal path and the optical memory path. The optical read/write controller is operable to selectively transmit light between the optical signal path and the optical memory path based on received control light.
In another aspect of the invention, an optical signal storage device includes an input optical port, an output optical port, an optical memory loop, and an optical read/write controller that is coupled between the optical memory loop and the input and output optical ports. The optical read/write controller comprises at least one saturable absorber optical switch having a transmittance that varies nonlinearly with received light intensity so that light is selectively transmittable between the optical memory loop and the input and output optical ports based on received control light.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.